Volcanic glass, such as perlite, forms when molten rock, i.e. lava, pours out of a volcano and rapidly cools. That rapid cooling inhibits crystal formation and permitting water to escape. Perlite is the lava that hardens immediately and contains 2-5% water.
Perlite is known in industry in two forms: crude and expanded. Crude perlite is prepared by the crushing and screening of perlite into various sized fractions. Expanded perlite is perlite after it has been heated. When heated, perlite can expand to as much as twenty times its original volume. This expansion is the result of heated water: when the glassy lava rock is heated to, for example, 890° C., the water molecules trapped in the rock turn into vapor which causes the rock to expand. That is similar to water that expands, when heated, in a corn kernel to create popcorn. It is the presence of these trapped water molecules in perlite which accounts for the physical properties of expanded perlite.
Expanded perlite can be manufactured to weigh between 32-240 kg/m3, making it adaptable for numerous applications in the construction, industrial, chemical, horticultural and petrochemical industries.
U.S. Pat. No. 7,736,574 discloses a method for the production of perlite products such as sheets, panels or bricks. The disclosed method involves first providing a quantity of expanded perlite and treating the perlite by applying a cement binder thereto, so as to at least partially encapsulate the perlite with binder. Thereafter, an amount of cement is added to the binder-treated perlite and a mixture is created. The described mixture is then formed and allowed to harden to yield solid articles. Nevertheless, the disclosed method is used for yielding perlite based solid articles.